Remove special case for libs when debuggable="true".

This causes confusion, is hard to debug (because the debuggable="true" behavior is more lenient), and doesn't have any obvious value (since it's trivially worked around by renaming "executable" to "libexecutable.so" anyway).

Flag: EXEMPT bugfix
Bug: https://issuetracker.google.com/160129591
Change-Id: I6a27a5b13df7bdc3fd3f76d8c8682867afded624